Earth Planets Space, 56, 429–446, 2004
Comparative petrogenetic investigation of Composite Kackar Batholithgranitoids in Eastern Pontide magmatic arc—Northern Turkey
Sabah Yılmaz Sahin1, Yıldırım Gungor2, and Durmus Boztug3
1 Istanbul University, Dept of Geophysical Engineering, 34320-Avcılar/Istanbul2 Istanbul University, Dept of Geological Engineering, 34850-Avcılar/Istanbul
3Cumhuriyet University, Dept of Geological Engineering, 58140-Sıvas
(Received August 9, 2003; Revised February 18, 2004; Accepted February 19, 2004)
The Pontides are an east-west trending orogenic belt which is subdivided into west, middle and eastern sectorsaccording to their different tectonostratigraphy. The Eastern Pontides are represented by west-east-trending tectoniczones resulted from a common Mesozoic-Tertiary history, comprises dominantly of magmatic rocks. The magmaticbelt in the Eastern Pontides includes a large batholith, termed the Composite Kackar Batholith (CKB) in which thereare various granitic facies. The emplacement of CKB occurred in pulses between the Early Cretaceous and Eoceneperiod during the development of the eastern Pontide magmatic arc and following collisional events. The membersof the CKB are Dereli-Sebinkarahisar (Giresun) in the west, southern Araklı (Trabzon) in the middle and KackarMountain and its surrounding area (Rize) in the east. The plutons ranging from syenite through monzonite togranite are typically medium-high K calc-alkaline rarely tholeiitic and metaluminous I-type. The studied membersof the CKB intrudes into the Late Cretaceous arc volcanics and are determined to be Late Cretaceous-Eocene(75.7 ± 1.55; 41.2 ± 0.89) in K-Ar age. The tectono-magmatic setting of the granitoids has been interpreted as anarc-related granitic suite, a post-collisional granitic suite and a post-orogenic granitic suite. Some plutons includingmafic magmatic enclaves (MME) and K-feldspar megacrystals suggest magma mixing/mingling. HFS and LILelement geochemistry of the granitic intrusions also suggest that fractional crystallization, magma mixing/minglingand crustal contamination played an important role in the evolution of the CKB. All the data mentioned aboveshow that the granitoids in the three different regions may have been derived from an arc, developed in response tothe northward subduction of the northern branch of neo-Tethyan oceanic crust beneath the Eurasian plate in LateCretaceous and a collision between the Pontide arc and the Anatolide-Tauride platform in Paleocene.Key words: Granite, Turkey, arc magmatism, collision; Eastern Pontides.
1. IntroductionThe Pontide tectonic belt of N Turkey is divided into three
segments: the western, central and eastern Pontides, basedon differences on pre-Jurassic basement units (Sengor andYılmaz, 1981; Yılmaz et al., 1997; Ustaomer and Robert-son, 1997; Okay and Sahinturk, 1997). The Eastern Pontidesis characterized by the Late Mesozoic-Early Tertiary mag-matic belt (Fig. 1), interpreted as a west-east trending con-tinental margin arc developed in response to the northwardsubduction of northern branch of neo-Tethyan oceanic crustbeneath the Eurasian plate in Senonian, while the formationof an Atlantic-type active continental margin (Yılmaz et al.,1997; Okay and Sahinturk, 1997; Ustaomer and Robertson,1997). In this region, The Eastern Black Sea Basin openedduring the Campanian-Maastrichtian through the rifting of amagmatic arc axis (Yılmaz et al., 1997; Okay and Sahinturk,1997). Closure of the Neo-Tethyan Ocean caused a collisionbetween the Pontide arc and the Touride-Anatolide platformin the Paleocene-Early Eocene. The effect of this collisioncontinued until the middle Eocene (Elmas, 1995; Yılmazand Boztug, 1996; Yılmaz et al., 1997; Okay and Sahinturk,
Copy right c© The Society of Geomagnetism and Earth, Planetary and Space Sciences(SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan;The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRA-PUB.
1997).In the Pontide arc, calc-alkaline magmatic activity be-
gan in the Turonian and continued intermittently till the endof the Paleocene. During the same period, granitic intru-sions were emplaced into the shallow levels of the crust andformed the first components of a composite pluton calledthe Rize granite (Cogulu, 1975; Taner, 1977; Tokel, 1995;Yılmaz et al., 1997). Emplacement of the pluton occurred inpulses and lasted until the late Eocene.
Magmatic rocks of different ages with various magmatichistories and different emplacement levels within the crustare exposed throughout the Pontide Belt. Granitic rocks inthe Eastern Pontides were described as “Kackar Batholith”by Pelin (1977) first and “Composite Kackar Batholith” byBoztug et al. (2001) subsequently. Either the various types ofgranitoids from granite to gabbro or the assorted magmaticevaluation terms like arc to collision, post collision and evenextensional regime magmatism derived from the direct man-tle material uplifting which aroused interest in the region.
According to some of the former studies it is put for-ward that the granitic rocks are composed of hornblende-biotite granite, granodiorite and quartz diorite, intruding intobasic volcanic rocks, and generally show a calc-alkalinetrend and have 65–95 Ma, of isotopic age (Cogulu, 1975;Taner, 1977; Gedikoglu, 1978; Moore et al., 1980; Okay
429
430 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
Giresun
Eynesil Rize
20 20040 40
km.
3932
TrabzonArsin
Pazar
Hopa
Batum
Artvin
Kelkit
Tortum
42
41
40
Dereli
Alucra
Sebinkarahisar
KesapMacka Çaykara
Gümüshane
Kaçkar
Ispir
Ardesen
Ikizdere
Arakli
1 2 3 4
N
WESTERN PONTIDES
EASTERN PONTIDESCENTRALPONTIDES
SAKARYA CONTINENT
IZMIR-ANKARA SUTURE ZONEKIRSEHIRMASSIF
T A U R I D E - A N A T O L I D E P L A T F O R M
A R A B I A N P L A T F O R M
MENDERES TAURUS BLOCK
ANKARA-ERZINCAN SUTURE ZONE
B L A C K S E A
EAAC
MEDITERRAIN SEA
NAF
ANKARA
TB
INTRA PONTIDE SUTURE
ISTANBUL ZONGULDAK ZONE
CAUCASUS
IM
Fig. 2a
Fig. 2b
Fig. 3
Fig. 4
GEORGIA
0
0
0
HopaSINOP
35.4 35.4
4 2
41.4
0
0
0
39 40 41000
0
GEORGIA
380
(a)
(b)
Fig. 1. (a) Major tectonic divisions of the Pontides and tectonic units of Turkey; IM, Istranca massive; TB, Thrace basin; AAZ, Armutlu-Almacık zone;KM, Kargı Massif; NAF, North Anatolian transform fault zone; EAAC, Eastern Anatolian accretionary complex (Yılmaz et al., 1997). (b) Locationmap of the studied area include three different area as the Dereli-Sebinkarahisar, Araklı and Kackar regions. 1. Paleozoic granitoids, 2. Late Cretaceousvolcanic-volcano-sedimentary rocks, 3. Late Cretaceous-Eocene granitoids, 4. Studied area.
and Sahinturk, 1997). The collision between the Anatolideand Pontide basements is suggested to have occurred some-time between Palaeocene (Yılmaz and Boztug, 1996) andearly Eocene (Sengor and Yılmaz, 1981; Yılmaz et al., 1997;Okay and Sahinturk, 1997), or the uppermost Cretaceous toearly Palaeocene (Yılmaz et al., 2000). Following this col-lision, an early to middle Eocene extensional regime tookplace in the Eastern Black Sea region. It has been explainedthat the extensional regime and associated magmatism inthe Eocene is related to the opening of the oceanic East-ern Black Sea Basin (Okay and Sahinturk, 1997; Kazmin
et al., 2000). Petrographical-geochemical and petrologi-cal properties of granitoids are explained in recent studies(Boztug et al., 2001; Boztug et al., 2002a, b; Yılmaz Sahin,2002, 2004). Granitoids outcropping from west to east in theDereli-Sebinkarahisar (Giresun) area, in the south of Araklıregion and in Kackar region are appreciated as the productsof CKB in the Eastern Pontides (Fig. 1) and have been in-vestigated for their different properties by many researchers(Yılmaz and Boztug, 1996; Gungor et al., 1997; Boztug etal., 2001; Boztug et al., 2002a, b; Yılmaz-Sahin, 2002).
The aim of this study is to evaluate the data of the previous
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 431
MEDITERANEAN SEA
ANKARA
SIVAS
GIRESUN
0 100 Km
NEASTERN PONTIDES
Güney Uzunalan
Meryemana
Fndkl
Karinca
Ikisu
Kayaalti
SusuzSürmen
Yüceköy
Pinarlar
Konuklu
Dogandüzü
Gökçebel
Çatak Y.
45 47 49 51 53 55 57
85
87
8937 39 41
91
93
95
97
99
37 39 41
03
05
47 49
07
51 53 55 57
N
0 1 2 Km
GEOLOGICAL MAP OF THE SOUTHERN PART OF DERELI TOWN (S GIRESUN)
EXPLANATIONS
43
C E
N O
Z O
I C
M E
S O
Z O
I C
T E
R T
I A
R Y
C R
E T
A C
E O
U S
J U
R A
S S
I C
PR
E-
JUR
AS
SIC
Ear
ly J
uras
sic
Late
Jur
as.
Late
C
reta
ceou
s-E
arly
Pal
eoce
neP
aleo
cene
- E
ocen
e
200016001200
Kk JgJd
Ka Ks
Kt SENW
Ty
Ts
Tg
Th
Te
Kka
KaKko
Ks
Kt
Kk
Jg
Jd
Jpo
Yücedere diorite/gabbro
Susuz conglomerate
Gökçebel syenite
Hanyani limestone
Kayaalti quartzolite
Aksu biotitemonzogranite
Sürmen granodiorite
Tamdere quartzmonzonite
Konuklu formation
Güney limestone
Disconformity
Pinarlar metamorphics
Tectonic contact
Kümbetobasivolcanics
Formations boundary
Strike slip faultTectonics contact
Village
Hanyani
A
A'
AA'
Egribelvolcanics
Dogandüzü formation
Figure 2a
Tamdere
Kümbet
Kurtulmus
(a)
Fig. 2. Geological map of (a) The southern part of Dereli town (South Giresun); (b) The northern part of Sebinkarahisar town (South Giresun) (Yılmaz,1995).
studies of the authors mentioned above, by explaining thesimilarities and differences of the plutonic rocks in termsof their age, magma types and geodynamic setting. Usingthe data from field mapping, petrography and whole rockgeochemistry, we have attempted to determine the tectono-magmatic evolution of the Eastern Pontides and to providebetter constraints of the geological evolution of Turkey.
2. Geological SettingThe granitoids of the Late Cretaceous to Eocene age
are subclassed in three plutonic phases and are describedin detail by Yılmaz and Boztug (1996) in the Dereli-Sebinkarahisar (DS) area (Figs. 2(a), (b)). The oldest unitof the DS region is the pre-Early Jurassic Pinarlar metamor-phite which may be compared with the various types of re-gional metamorphic rocks (Topuz et al., 2004) of Pulur mas-sive in the Eastern Pontides (Okay and Sahinturk, 1997). Theearly Jurassic Doganduzu formation, including volcanic-
volcano-sedimentary rocks, tectonically overlays the meta-morphic outcrops both in the Dereli and Sebinkarahisar ar-eas. Uzunalan phyllonite is the third unit that was formedbetween Pinarlar metamorphic and Doganduzu formationdue to the NE-SW faulting system (Fig. 2(a)). The plu-tonics cut all these units. Previously, plutonic rocks wereseparated into three phases by Yılmaz and Boztug (1996),but later new radiometric ages (hornblende K-Ar) and cool-ing ages by apatite fission-track method (Boztug et al.,2002a) required a revision. The first plutonic phase is LateCretaceous in age, is syenitic-monzonitic in character andconsists of Sebinkarahisar quartz syenite, Gokcebel quartzsyenite and Tamdere quartz monzonite. Late CretaceousAksu biotite monzogranite and Surmen granodiorite are de-fined as the second plutonic phase. These rocks intrudeinto the Late Cretaceous Konuklu and Kumbetobası forma-tions of volcanic-volcano sedimentary rocks. Yucedere dior-ite/gabbro of the middle Eocene age is the third plutonic
432 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
(b)
Fig. 2. (continued).
phase in the area. The youngest units of this region arethe Miocene Tamzara formation and the Mio-Pliocene Hack-ayası volcanics (Fig. 2(b)).
The Araklı region (A) located in the westernmost partof the Kackar Batholith is evaluated within the magmaticassociation in the Eastern Pontide Magmatic Belt (Fig. 3;Yılmaz-Sahin, 2002). The oldest unit of this region is Early
Jurassic basement metamorphic rocks, similar to the Pu-lur metamorphics and which is exposed in a very limitedarea. These rocks are disconformly covered by the LateCretaceous volcanic-volcanosedimentary rocks called as theTaslıyayla volcanics including submarine basaltic-andesiticlavas, its pyroclastic products and carbonate-marl succes-sions. Plutonic rocks of three different magma sources
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 433
Fig. 3. Geological map of the south Araklı (Trabzon) region (Yılmaz-Sahin, 2004).
intrude into the Taslıyayla volcanics: Those are the LateCretaceous-Early Paleocene Gundogdu altered microgran-ite, Bogalı K-feldspar megacrystalline monzogranite and theEocene Uzuntarla porphyritic granodiorite. The youngestunit of this region is the Ocaklı andesite (Yılmaz-Sahin,
2004; Fig. 3).Three magmatic pulses comprising four plutonic units
have been described at the main axis of the Kackar Batholith,in the most recent studies (Gungor, 1997; Fig. 4). Theseplutonics in the Kackar region called as Marselavat quartz
434 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
Ayder K-feldsparmegacrystallinegranodiorite
Marselavatkuvars monzodiyorite
Hemsindere Formation
Sasmistal microgranite
Halkalitas granodiorite
EXPLANATIONS
LAT
E C
RE
TAC
EO
US
-E
AR
LY P
ALE
OC
EN
EM
IDD
LEE
OC
EN
ELA
TE
CR
ETA
CE
OU
S
Valley
Lake
Formation boundary
Daval D.
GEOLOGICAL MAP OF THE MIDDLE PART (YUSUFELI-ÇAMLIHEMSIN-ISPIR) OF THE KAÇKAR BATHOLITH
N
Büyük Ç
ay
Olgunlar
Sirakonaklar
Asagi Kaçkar Y.Kaçkar D.
Topluca Y.K
avra
n D
.
Palakçur Y.
Asagi Kavran Y.
Yukari Kavran Y.
Lodicur Y.
SOG
ANLI
DAG
I
3527
m.
Kindavul T.3562 m.
Palakçur D.
ALTIP
ARMAK D
AGI
460
m.
Asagi Çaymakçur Y.
Yukari Çaymakçur Y.
KAÇ
KA
R D
AGI
3932
m.
0 1 2km.
MEDITERANEAN SEA
ANKARA
SIVAS
RIZE
0 100 Km
EASTERN PONTIDES
Figure 4
Fig. 4. Geological map of the middle part (Yusufeli-Artvin, Camlıhemsin-Rize, Ispir-Erzurum) of the CKB (Gungor, 1997).
monzodiorite, Ayder K-feldspar megacrystalline granodior-ite, Sasmistal microgranite and Halkalıtas granodiorite, in-truding into the Hemsindere formation, aged from Late Cre-taceous to Late Eocene.
The first magma pulse: Marselavat unit of the LateCretaceous-Early Tertiary age is represented by the activityof monzonitic rocks.
The second magma pulse: Ayder unit of the Paleocene ageand its highly fractionated product Sasmistal unit.
The third magma pulse: The youngest unit in the wholeregion; Halkalıtas unit of the Late Eocene age (Fig. 4).
The plutons of CKB commonly intrude into Late Creta-ceous volcanic rocks. They sometimes cause contact meta-morphism in their wall rocks. Tectonically, E-W direction
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 435
100 200 300-100-300-4000
-200 0
Q=
Si/3
-(K
+N
a+2C
a/3
300
200
100
P=K-(Na+Ca)
1234
5678
12 11 10 9
*x
+
+
Aksu biotitemonzograniteSürmengranodiorite
Tamdere quartzmonzoniteGökçebel quartzsyeniteSebinkarahisarquartz syenite
Uzuntarla porphyriticgranodiorite
Halkalitasgranodiyorite
Sasmistalmicrogranite
Marselavat quartzmonzodiorite
*
Yücedere d/go +
Bogali K-feldsparmegacrystallinemonzogranite
PO
ST
-CO
LLIS
ION
GR
AN
ITIC
SU
ITE
Ayder K-feldsparmegacrystallinegranodiorite
x
AR
C-R
ELA
TE
D G
RA
NIT
IC S
UIT
E
*
PO
ST
-OR
OG
EN
IC
GR
AN
ITIC
SU
ITE
Fig. 5. Chemical nomenclature diagram (Debon and Le Fort, 1983) of the rock samples of some plutons of Dereli-Sebinkarahisar, Araklı and Kackarregions from the Kackar batholith.
thrusting faults and NE-SW direction diagonal faults formedunder the effect of a N-S compression regime might havecaused the intrusions of the plutons. According to geologi-cal properties; the pluton occurs in the three different areasof CKB may have different emplacement levels.
3. Intrusive PetrographyThis study is supported by the previous major studies done
(Yılmaz and Boztug, 1996; Gungor et al., 1997; Boztug etal., 2001; Yılmaz and Sahin, 2002) in the three different re-gions in order to compare the granitoids in terms of petrog-raphy.3.1 Dereli-Sebinkarahisar region
The properties of the DS granitoids of the three plutonicphases are suggested to be valid for all the granitoids namedas Composite Kackar Batholith (Yılmaz and Boztug, 1996).The first plutonic phase consists of Sebinkarahisar quartzsyenite, Gokcebel quartz syenite and Tamdere quartz mon-zonite. According to the classification diagram (Debon andLe Fort, 1983); they are defined as syenite, quartz syeniteand quartz monzonite (Fig. 5). The syenites are holocrys-talline, medium to coarse grained, equigranular textured andmineralogically consist of alkaline feldspar (orthoclase andperthite), plagioclase, augite, hastingsite, arfvedsonite andquartz. Sphene, apatite, zircon and opaque minerals accom-pany the syenites as accessories. Tamdere quartz monzoniteis medium-coarse grained and equigranular textured. Ac-cording to the classification diagram (Debon and Le Fort,1983) it is formed of quartz monzodiorite, quartz monzonite,granodiorite and adamellite (Fig. 5). Mineralogically, it con-sists of alkaline feldspar (orthoclase and microcline), pla-gioclase, quartz, hastingsite, augite and biotite; also apatite,epidote, zircon and opaque minerals as accessories. Thesecond plutonic phase is constituted of granodiorite, mon-
zogranite and adamellite of Aksu biotite monzogranite andSurmen granodiorite (Fig. 5). Feldspars (commonly pla-gioclase (An25−40)) abundance in adamellite, occurrence ofquartz and biotite, hornblende abundance in granodiorite andthe presence of allanite makes out the mineralogical differ-ences. The third plutonic phase is Yucedere diorite/gabbroand consists of diorite, quartz diorite and gabbro. Mineralog-ically it is composed of augite, hornblende and plagioclase(An35−50).3.2 Araklı region
Gundogdu altered microgranite; the first unit of plutonicrocks (Fig. 3) in the South of Araklı differs from other rocksby its common aphanitic-porphyritic texture and graphic–myrmekitic texture. Alteration is mostly common in everyrock such as rhyolite, porphyritic granite, aplite and gra-nophyre dykes. Due to this common alteration, secondaryminerals as carbonates, chlorites, epidotes and muscovitesare formed. On account of this common alteration, wholerock geochemical analyses could not be done for the rocksof the unit except for the Bogalı and Uzuntarla rocks (Ta-ble 1). Bogalı K-feldspar megacrystalline monzogranite issituated in the adamellite area in the Q-P chemical nomen-clature diagram (Fig. 5). These rocks are defined as por-phyritic textured due to the presence of K-feldspar megacrys-tals and they contain mafic microgranular enclaves (MME)(Didier and Barbarin, 1991) and some special mixing tex-tures (Hibbard, 1991, 1995) such as antirapakivi texture,spongy cellular dissolution/melting plagioclase and smalllath-shaped plagioclase within large plagioclase. K-feldspar(orthoclase), plagioclase, hornblende, biotite and accessoryapatite, titanite, zircon and opaque minerals are observed.Uzuntarla porphyritic granodiorite has a porphyritic texturewith a fine grained matrix including plagioclase, quartz, or-thoclase, hornblende, biotite and phenocrystals of plagio-
436S.Y
.SAH
INetal.:
CO
MPA
RA
TIV
EPE
TR
OG
EN
ET
ICIN
VE
STIG
AT
ION
OF
GR
AN
ITO
IDS
INE
AST
ER
NPO
NT
IDE
SM
AG
MA
TIC
AR
C
Table 1. Averages and standart deviations of the whole-rock major (wt %) and trace (ppm) chemical compositions of the various plutons ofDereli-Sebinkarahisar, Araklı and Kackar regions.
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 437
Tabl
e1.
(con
tinue
d).
438 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
40 45 50 6055 65 70 75 80
Subalkaline
SiO2 (wt %)
AlkalineNa2
O+
K2O
(w
t %)
2
4
6
8
10
12
16
18
20
14
035
45 55 65 75
SiO2 (wt %)
K2O
(w
t %)
0.5
1
1.5
2
2.5
3
4
4.5
5
3.5
0
Low-K
Medium-K
High-K
**
x
*
* x
+ +
F
A M
Tholeiitic
Calc-alkaline
**
x
++
c)
b)
a)
Fig. 6. (a) Total alkali vs. silica (Irvine and Baragar, 1971); (b) K2O vs. silica (Peccerillo and Taylor, 1976) (c) AFM diagrammes (Irvine and Baragar,1971) of the rock samples of some plutons of Dereli-Sebinkarahisar, Araklı and Kackar regions from the Kackar batholith. See Fig. 5 for explanation ofsymbols.
clase. The precence of corroded quartz just like in Bogalıunit is also a characteristic property of these rocks. Hy-drothermal alteration is very common. As a result of al-teration, secondary chlorite, epidote and clay minerals areobserved.
3.3 Kackar regionGranitoids in Kackar region from gabbro to granite in
composition, originated from different magma sources andunder various interaction processes between felsic and maficmagmas (Gungor et al., 1997; Boztug et al., 2001, 2002a,b). In this study, four units belonging to Kackar batholith
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 439
Al2
O3/
(Na2
O+
K2O
)
Al2O3/(CaO+Na2O+K2O)
PeraluminousMetaluminous
Peralkaline
1 2
1
2
3
*
x
*
1.2
1.1
1.0
0.9
0.8
0.7
0.645 50 55 60 65 70 75 80
SiO2
A/C
NK
*
+
x
+
*
Arc-re
late
d
gran
itic s
uite
Post-orogenic
granitic suite
Post-co
llision
granitic su
ite
a)
b)
Fig. 7. (a) Al2O3/(Na2O+K2O) vs. Al2O3/(CaO+Na2O+K2O) diagram (Maniar and Piccoli, 1989); (b) ASI vs. SiO2 diagram of plutons of CKB. SeeFig. 5 for explanation of symbols.
are dealt with and compared with the plutons in the west.These plutons are Marselavat quartz monzodiorite, Ayder K-feldspar megacrystalline granodiorite, Sasmistal microgran-ite and Halkalıtas granodiorite. Marselevat quartz monzodi-orite and are mostly located in the quartz monzodiorite re-gion but some of the samples are located in the quartz mon-zonite, granodiorite and adamellite region in the QP clas-sification diagram (Fig. 5). The moderate-coarse grained,equigranular textured Marselavat unit contains hornblende,biotite and clinopyroxene as mafic minerals; MME’s as ev-idence of magma mingling and also antirapakivi, poikili-tik K-feldspar textures as some special mixing textures areobserved. Ayder K-feldspar megacrystalline granodioritewhich includes K-feldspar megacrystal of about 0.5–3 cmin diameter, are mostly porphyritic, less equigranular- andthought to be generated from the different magma sourcethan that of Marselavat unit in Kackar Batholith. In theQP classification diagram they are situated in the granodi-orite, adamellite and granite area (Fig. 5). Especially in gra-
nodiorites there are hornblende and clinopyroxene besidesbiotite. Not only the presence of K-feldspar megacrystals,but also the existence of MMEs, proves the mixing/minglingof mafic and felsic magmas. In addition, antirapakivi tex-ture, poikilitic/oikocrystic K-feldspar, spongy cellular disso-lution/melting plagioclase and boxy cellular growth plagio-clase textures are observed as the evidence of magma mix-ing. Entirely granitic Sasmistal microgranite is a fraction-ation product that is emplaced in a subvolcanic position ofAyder unit. It shows mostly phaneritic and less aphanitic,fine-grained texture and vein type occurrences. Rocks in-clude quartz, orthoclase, plagioclase and a small amount ofbiotite. Related to post-orogenic extension, Halkalıtas gra-nodiorite generated from the third magma source, intrudedinto shallow crustal levels as the forms of small stocks orsometimes N-S, NE-SW, NW-SE and E-W trending veinrocks. This unit is late Eocene in age and porphyritic rockscontain coarse plagioclase (An35−50), hornblende and pyrox-ene phenocrysts in a fine matrix of feldspar and mafic min-
440S.Y
.SAH
INetal.:
CO
MPA
RA
TIV
EPE
TR
OG
EN
ET
ICIN
VE
STIG
AT
ION
OF
GR
AN
ITO
IDS
INE
AST
ER
NPO
NT
IDE
SM
AG
MA
TIC
AR
C
Table 2. Rock types, magma series, magmatic processes, geodynamic setting, K-Ar age dating (hornblende minerals) and apatite-sphene-zircon fissiontrack analyses results of various plutons of Dereli-Sebinkarahisar, Araklı and Kackar regions.
mingling
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 441
50 90 170130 210 24010
70
170
270
370
470
570
20 40 60 80 1000
115
15
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315
415
515
250
180
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20
60
140
220
Zr
(ppm
)
K/R
bK
/Rb
Rb (ppm)
K/Ba
SiO2 (wt %)
80706050 55 65 7545
** x
* *x
**
x
++
++
+
+
Halkalitas
GökçebelM
arse
lavat
Aksu AyderSürmen
Uzuntarla
Sürmen
Uzuntarla
HalkalitasAyder
**
x
5
4
3
2
1
050 10 15 20 25 30
Y/N
b
Zr/Nb
+
cc
6
a)
d)c)
b)
FC FC
FC
Post-orogenicgranitic suite
Arc-relatedgranitic suite
Post-collisiongranitic suite
Fig. 8. Some LILE and HFSE variation diagram of the some plutons of Dereli-Sebinkarahisar, Araklı and Kackar regions. FC, fractional crystallization;CC, Crustal contamination. See Fig. 5 for explanation of symbols.
erals.When the petrographical properties of the plutons of the
three different regions are compared to each other (Table 2),Sebinkarahisar and Gokcebel units are similar but displaydifferences from the Dereli-Sebinkarahisar area. There isnot another unit similar to these plutons at the eastern part ofKackar Batholith, whereas Tamdere unit is like Marselavatunit in the Kackar region. Surmen granodiorite resemblesUzuntarla porphyritic granodiorite and Halkalıtas granodior-ite, but shows textural and genetic differences from the rest.Bogalı and Ayder units are similar to each other in terms ofrock-type but differ in their time of formation (Table 2).
4. Comparision of the Geochemical Features of thePlutons
The whole rock major and minor element analyseswere done with the Rigaku-3270 E-WDS XRF spectrom-eter using USGS and CRPG rock standards (Govindaraju,1989) for calibration at Cumhuriyet University Mineralogy-Petrography Research Laboratory (MIPJAL) and at ACME(ACME Analytical Laboratories Ltd., Canada), K-Argeochronological studies at Israel Geological Survey and theapatite-sphene-zircon fission-track studies were held at MaxPlanc Instute in Hielderberg-Germany. A deal of whole rock
major and minor element chemical analyses are evaluatedby the Debon and Le Fort (1983) nomenclature diagram andthen their average values (n) and standard deviations are cal-culated (Table 1).
The geochemical studies clarify the characters of thethree plutonic phases in the Dereli-Sebinkarahisar region:The first phase is subalkaline–trans-alkaline, high-K calc-alkaline, the second phase is entirely subalkaline and thethird phase is subalkaline-low-K tholeiitic (Figs. 6(a), (b),(c)). According to alumina saturation index (ASI) byShand’s (1947), most of the plutons of Dereli-Sebinkarahisarregion are metaluminous except to Aksu biotite monzo-granite (Maniar and Piccoli, 1989; Table 1; Fig. 7(a)).Arc, post-collision and post-orogenic associations are shownA/CNK-SiO2 diagram (Fig. 7(b)). Aksu unit is a weaklyperaluminous felsic I-type granite similarly to the ones—resultant largely from partial melting rather than fractionalcrystallization—in the Lachlan Fold Belt, (Chappell, 1999).According to the K/Rb-Rb, K/Rb-K/Ba and Zr-SiO2 dia-grams, every three plutonic phase originated from differ-ent magma source and particularly the first and the sec-ond phases arose due to fractional crystallization (Figs. 8(a),(b), (c)). The Y/Nb and Zr/Nb diagram is used to con-sider the degree of crustal contamination (Wilson, 1989).
442 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
500 1000 1500 2000 2500 3000
500
1000
1500
2500
2000
1. Mantle Fractionates2. Pre-plate collision3. Post-collision Uplift4. Late orogenic5. Anorogenic6. Syn-collision7. Post-orogenic
1
2
3
4
5
R1=4Si-11(Na+K)+2(Fe+Ti)
00
R2=
6Ca+
2Mg+
Al
**
x
+
+
6
7
*
1 10 100
1
10
100 1000
Rb/
Zr
Nb (ppm) Y (ppm)
* **
0.1
Primitive island arcs orcontinental margin arc Normal continental arc Mature continental arc
Arc matu
rity
1
10
b)
a)
Fig. 9. (a) R1–R2 major element geotectonic discrimination diagram (Batchelor and Bowden, 1985) of the some plutons of Dereli-Sebinkarahisar, Araklıand Kackar regions. (b) Rb/Zr vs Nb, Y diagrams (after Brown et al., 1984) for some units (Sebinkarahisar, Gokcebel, Tamdere, Surmen, Aksu, Bogalıand Marselavat). See Fig. 5 for explanation of symbols.
In this diagram, the first, second and third phases show noor slight contamination (Fig. 8(d)). In the R1–R2 geotec-tonic discrimination diagram (Batchelor and Bowden, 1985),units of the first phase like Sebinkarahisar and Gokcebel aresituated in the post-collision uplift field whereas Tamderequartz monzonite is situated in the pre-plate collision field(Fig. 9(a)). Though the three units are the products of arcmagmatism, because of the alteration, they are located in thepost-collision uplift field in this diagram. Surmen granodi-orite of the second phase is located in the pre-plate collisionfield whereas Aksu biotite monzogranite plots near the areaof syn-collision (Fig. 9(a)). Yucedere diorite/gabbro is lo-cated in the mantle fractionates field due to its M-type origin(Fig. 9(a)). In Nb-Rb/Zr and Y versus the Rb/Zr diagrams(Brown et al., 1984), four plutons of Araklı region plot innormal arc area, two plutons (Tamdere and Surmen) plot in
primitive arc-normal arc transition (Fig. 9(b)). Rb, K, Th, Ydisplay higher values than Ti in MORB normalized diagrams(Fig. 10).
Studies in the Araklı region point out that Bogalı andUzuntarla units present differences in terms of geochemistryas well as their geodynamic position. Both units are subal-kaline and each presents high-K calc-alkaline and moderate-high-K calc-alkaline, respectively (Figs. 6(a), (b), (c)).Granitic rocks of Araklı region are metaluminous based onthe Al2O3/(Na2O+K2O) versus Al2O3/(CaO+Na2O+K2O)diagram (Maniar and Piccoli, 1989; Fig. 7(a)). ASI values ofthe plutons range from 0.82 to 0.99 (Table 1; Fig. 7(b)). Inthe K/Rb-Rb, K/Rb-K/Ba and Zr-SiO2 diagrams, fractiona-tion trends are clearly identified (Figs. 8(a), (b), (c)). In theY/Nb- Zr/Nb diagram the trend indicates crustal contami-nation (Fig. 8(d)). Bogalı unit takes place in a post-collision
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 443
Fig. 10. Rock/MORB diagrams of some plutons of Dereli-Sebinkarahisar, Araklı and Kackar regions.
uplift area but Uzuntarla unit is settled at a pre-plate collisionarea based on R1–R2 diagram (Fig. 9(a)). Some samples ofBogalı unit plot in a normal arc area, as the others plot ina mature-arc area at the Nb-Rb/Zr and Y versus Rb/Zr di-agrams (Fig. 9(b)). There are clear negative anomalies inRock/MORB diagrams of Bogalı and Uzuntarla units in Th,Nb and Ti values (Fig. 10).
Granitoids from three different magma sources in theKackar region represent differences in geochemical charac-teristics. Marselavat, Ayder with Sasmistal and Halkalıtasunits are classified as the first, second and third mag-matic pulses, respectively (Gungor, 1997; Gungor et al.,1997). The first and the second magmatic pulses are sub-alkaline, high-K calc-alkaline whereas the third pulse rep-resents subalkaline, weakly tholeiitic and moderate-high-Kcalc-alkaline properties (Figs. 6(a), (b), (c)). Most sam-ples of the units are plotted in metaluminous areas in theAl2O3/(Na2O+K2O) versus Al2O3/(CaO+O+Na2O+K2O)diagram (Maniar and Piccoli, 1989) except for Ayder unit(Fig. 7(a)). ASI of all of the units are <1.1 (Table 1)and show a fractionation trend in ASI versus SiO2 diagram(Fig. 7(b)). In the diagrams of K/Rb-Rb, K/Rb-K/Ba andZr-SiO2, Marselavat and Halkalıtas units show crystalliza-tion properties themselves. Sasmistal microgranite of thehighly fractionated Ayder unit has a clear fractionation trend(Figs. 8(a), (b), (c)). In the Y/Nb-Zr/Nb diagram the crustalcontamination trend is seen in all of them (Fig. 8(d)). In the
R1–R2 geotectonic discrimination diagram, Marselavat is lo-cated in the pre-plate collision and Ayder and Sasmistal inthe collision related region (Fig. 9(a)). Halkalıtas granodior-ite is located in the arc related region (Fig. 9(a)). Some sam-ples of Marselavat unit plot in normal-arc area in the Rb/Zr-Nb and Rb/Zr-Y diagrams (Fig. 9(b)). The values of ele-ments like Th, K, Sr, Zr, Y and Ti show positive anomaly inRock/MORB diagrams. Similar characteristics are observedfor Ayder and Sasmistal units. Besides, more fractionationcauses a general decrease in the whole elements of Sasmistalunit (Fig. 10).
When the plutons of the three regions are comparedin terms of geochemistry; Tamdere, Marselavat, Uzuntarlaunits and Halkalıtas granodiorite present parallel fraction-ated trends in some of the fractional crystallization dia-grams such as K/Rb-Rb, K/Rb-K/Ba and Zr-SiO2 (Figs. 8(a),(b), (c)). In crustal contamination diagrams as Zr/Nb-Y/Nb, Ayder, Bogalı and Uzuntarla units seem to be muchmore contaminated than Halkalıtas and Marselavat units butSebinkarahisar, Gokcebel, Aksu and Yucedere units are theleast contaminated by crustal material (Table 2, Fig. 8(d)).In the R1–R2 diagram; the majority of units take place inpre-plate collision area whereas a small part of the unitsare settled in post-collision uplift and collision related area(Fig. 9(a)). These units are not evaluated only by these dia-grams, but are also considered according to the situation oftheir regional geological setting and geochronological ages
444 S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC
(Table 2). For example, though Halkalıtas granodiorite isin the arc related region, it is thought to be a product ofan old arc relevant to uplift after collision (Fig. 9(a)). Al-though most of arc related plutons are plotted in the nor-mal arc area in the Rb/Zr-Nb and Rb/Zr-Y diagrams, someof them are plotted a normal arc-mature arc transition area.Only Tamdere unit settled in a primitive arc area (Fig. 9(b)).The plutons have properties resembling genetic and elemen-tary behavior in Rock/MORB diagrams. For example, ele-ment behavior trends of Tamdere resemble arc related plu-tons, similar to trends of Marselavat unit (Fig. 10). Someelements such as Th, K, Sr and Zr show positive anomalywhereas others as Ba, Nb and Ti show negative anomaly inthese diagrams. These types of element behaviors are seenat the active continental margins (Wilson, 1989). The dis-play of values which are enriched in crustal originated el-ements such as Rb, K, Th, Y than in mantle derivate ele-ments such as Ti and P (Mason and Moore, 1982; Wilson,1989) in MORB normalized diagrams support arc magma-tism with excess crustal contribution (Fig. 10). Yucedere andHalkalıtas units present similar properties, especially, Sr, Zr,Ti and Y elements which are depleted than the Rb, Ba andTh elements (Fig. 10).
5. Discussion and ConclusionsArc related calc-alkaline magmatism in Eastern Pontides
began during the Turonian and continued till the end of thePaleocene (Tokel, 1995; Yılmaz and Boztug, 1996; Gungoret al., 1997; Okay and Sahinturk, 1997; Yılmaz et al., 1997;Yılmaz et al., 2000; Boztug et al., 2002a, b). During thesame period granitic rocks of CKB kept intruding into thecalc-alkaline volcanic rocks. Arc related granitic suite iscalkalkaline, high-K subalkaline, hybrid and mostly meta-luminous except Aksu unit which is slightly peraluminousand I-type in character (ASI < 1.1). This I-type characterdiffers from fractionated and unfractionated I-type LachlanFold Belt granitoids (Chappell, 1999), for its distinctly highSr and lower SiO2 values. Due to this difference CKB maybe suggested to be derived from hybrid magma formed frommantle and crust.
Different types of mafic microgranular enclaves (MME)and some special microscopic textures indicating magmamingling and magma mixing reflect a voluminous hybridiza-tion in the genesis of the magma source of the granitic suites.MMEs, especially, represent the hybrid liquids formed by themixing of mantle derived magma with lower crustal melts.
The CKB granitoids derived from Eocene post-collisionmagmatism are called as post-collision granitic suite. Thecollision of the Pontide and Anatolide basements beganaround the Paleocene in the Eastern Pontides (Yılmaz andBoztug, 1996) and formed Uzuntarla unit, Ayder, and itshighly fractionated derivative Sasmistal unit in the studiedarea.
Post-collisional magmatism might have been derived fromthe crustal rocks and the underplating mafic magma source.It is generally accepted that underplating and emplacementof significant volumes of hot basaltic liquids into the lowercrust or at the crust-mantle interface may supply the heatneeded to initiate and promote large scale crustal anatexis ina continental collision zone (Dewey et al., 1988; Bergantz,
1989). Peraluminous Ayder unit similar to the I-type Huang-bai granites from Central China (Chen et al., 2002) is an ex-ample of this type of magma genesis.
After the crustal thickening, following this collision, anearly to middle Eocene extensional regime occurred inEastern Pontides resulting deformation of a post-orogenicgranitic suite composed of Yucedere and Halkalıtas units inCKB. These are tholeiitic, low-K, M-type and subalkaline,middle-high potassic, calcalkaline, hybride and I-type char-acter, respectively.
Subsequent post-orogenic magmatism comprising entirelyintraplate magmatic suites generally occurred from a new un-depleted and enriched mantle source (Bonin et al., 1998).The Dabie UHP complex in Central China (Chen et al.,2002) is one of these types. Mantle-derived mafic/ultramaficmagmas intruded into the thickened continental crust in thegranitoids of Central China (Chen et al., 2002); In contrast,however, Yucedere unit intruded into the thinning continen-tal crust, by extensional regime in post orogenic suite ofCKB.
The intrusion of mantle derived mafic magma withinthe crust accompanied by extensive interaction with crustaland mantle derived melts produced hybrid parental magmawhich formed Halkalıtas Unit.
All these intrusive suites representing various stages ofa convergence system, i.e. subduction, post-collisional andpost orogenic, are considered to be related to the evolutionof the northward subduction of the northern branch of theneo-Tethyan Ocean beneath the Eurasian continent along theAnkara-Erzincan suture zone and subsequent compressionaland extensional tectonic regimes.
The granitoid and the country rock studies done in thethree different areas in the Eastern Pontides points out theresults below;
• Arc related granitic suite is composed ofSebinkarahisar, Gokcebel, Tamdere, Surmen, Aksu,Bogalı and Marselavat units. These units mighthave been crystallized from different magma sourcesunder the effects of different magmatic processes(i.e. fractional crystallization, partial melting, crustalcontamination, magma mixing/mingling), and they ex-hibit subalkaline, metaluminous, high-K, calkalkaline,I-type properties.
• Post-collision granitic suite comprises Uzuntarla, Ay-der and Sasmistal units. Petrological features of thissuite resemble the arc related granitic suite. Only themagma source of this suite presents differences from theother suites. The presence of K-feldspar megacrysts andMMEs in both of these suites suggest a hybrid magmasource formed by the mixing of felsic and mafic mag-mas.
• Post-orogenic granitic suite consisting of Yucedere andHalkalıtas units were formed under the extensionalregime in Eastern Pontides. These units are tholeiitic,low-K, M-type and subalkaline, middle-high-K, calc-alkaline, hybrid and I-type character, respectively.
• Bogalı and Uzuntarla units in Araklı region yield some
S. Y. SAHIN et al.: COMPARATIVE PETROGENETIC INVESTIGATION OF GRANITOIDS IN EASTERN PONTIDES MAGMATIC ARC 445
hornblende K-Ar ages ranging from 75.7 ± 1.55 to61.4 ± 1.47 Ma and from 42.4 ± 0.87 to 41.2 ± 0.89Ma, respectively (Table 2).
• The plutons, outcropped in Kackar region are derivedfrom three different magma sources and are comprisedof different aged granitoids. One of these plutons is theLate Cretaceous-Early Tertiary (Paleocene) Marselavatunit displaying subalkaline, high-K calkalkaline, arc re-lated character. Paleocene Ayder unit which is com-prised of a different magma source, and its highlyevolved fractionated derivative Sasmistal unit have sub-alkaline, high-K calc-alkaline, post-collision relatedmagma genesis. The third and latest unit is the LateEocene Halkalıtas granodiorite which has middle-highK. The majority of samples are calc-alkaline, post oro-genic extensional regime.
• Late Cretaceous–Paleocene Sebinkarahisar, Gokcebel,Tamdere Aksu, Surmen, Bogalı and Marselavat unitshave arc character. On the other hand, Paleocene-Eocene Uzuntarla, Ayder and Sasmistal units have postcollision character. Yucedere and Halkalıtas units havepost orogenic rifting features.
Acknowledgments. This study was supported by the ResearchFund of Istanbul University, project number: 1263/050599 and bypartly the Research Foundation of Cumhuriyet University. The au-thors also thank the General Directorate of Mineral Research andExploration (MTA), Trabzon, for partial logistical support duringfield work. The authors are grateful to Prof. Dr. Milan Kohud andProf. Dr. Tetsuichi Takagi for the constructive and valuable com-ments.
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